The present invention relates to a device for regulating or respectively limiting at least one temperature value or temperature range of radiation or contact heating in electric cooking apparatus, and wherein at least one temperature sensor is provided for regulating or limiting the temperatures, the sensor having a rod of high thermal expansion which is disposed in a tube of low thermal expansion, the tube being held between holding parts.
The regulating or limiting of the temperature in a device of the above-mentioned type is effected, in particular, in a manner wherein a temperature-induced axial movement of the rod-shaped temperature sensor is used to actuate the contact system, and in that a heating circuit is connected at a given temperature and then disconnected at a given higher temperature.
Since the temperatures to be measured lie within the range of up to 800.degree. C., relative movement in a radial direction can take place in the region of a contact surface of the end of the tube, which movement may involve a rubbing between a stationary and a moving element. The tube is preferably formed of quartz glass, with an adjoining holding part which consists preferably of metal, the relative movement is a result of different coefficients of expansion. As a result of frequent moving back and forth, there results after lengthy use a higher frictional resistance caused by rubbing-in, and finally a splintering off of the end of the tube.
On the other hand, it has also been observed that splintering can occur even upon initial use due to a rough surface of the quartz tube.
The object of the present invention is to create a device for regulating or limiting at least one temperature value or temperature range of the above-described device in which damage caused by alternate temperature stresses, in particular the splintering-off of the tube ends, is dependably prevented.